The invention relates to a device having locking blades disposed in the peripheral channel of a turbojet-engine disk, the blades include roots of a hammer attachment type which are insertable through a window into the channel and are kept therein by geometrically interlocking with the channel""s sidewalls. The locking device is inserted through the loading window into the channel and includes a locking element which can be positioned into a lock housing in sidewalls of the channel by means of a radial drive bolt of which the head rests against the bottom of the channel.
Several locking elements per stage may be used. In general the bolthead, which is wider than the shank, is housed in a depression in the channel bottom opposite the corresponding lock housing. Because the bolthead is wider than the shank, the bolt is always retained. In present-day designs, the locking element consists of a salient on the upper side of a case which, in a locked position, rests against the channel sidewalls near the throat of the channel. This case comprises a lower base which is positioned away from the bolthead in order to allow the case to slide inside the channel when the blades are being assembled. In order to achieve sliding, the salient on the case must be situated inside the channel, and the base of the case should rest against the bolthead and be situated near the bottom of the channel.
When the device is situated opposite the lock housing, as a result of the rotation of the blade assembly about the disk, the case rises outward on account of the drive bolt being operatively moved by a wrench. The salient is kept in the lock housing by being braced on one hand between the latch case resting in the disk throat and on the other hand the bolthead housed in a depression at the channel bottom. The system operates in bolt/nut manner and is slowed either by local deformation, a projecting thread or any other means.
If the bracing effect should be lost, only the self-locking feature retains the bolt and prevents the salient from escaping from the lock housing.
By its intrinsic design, the integral unit consisting of the case and its salient is devoid of constraining guide elements when it slides in the channel during assembly. Accordingly, the bolthead might become improperly positioned in its depression during the tightening phase and as a consequence, the bolthead subsequently might move during turbojet-engine operation and the bracing effect might be lost. Tightening a poorly positioned bolt also may entail jamming the thread and keep the salient in the lock housing, ultimately causing difficulties in disassembling the device for maintenance work.
Moreover, when the turbojet engine is operational, the bolt is subjected to substantial centrifugal forces which, if the bracing effect were lost, may rotate this bolt which may enter the gas stream, and in the long run, the salient might then be released from the lock housing when the turbojet engine is stopped.
The objective of the invention is a locking device which in the operational mode of the turbojet engine, retains locking blades within the channel, and which prevents seizing during assembly.
The invention attains this goal in that the locking element is mounted in an axially sliding manner in a radial aperture of a case of which the cross-section matches that of the channel. The bolthead is trapped between the channel bottom and the case base.
Accordingly, when sliding in the channel, the case is constrained by being guided, and as a result, the bolt axis reliably is held in an axial direction. Moreover the bolthead is radially stationary relative to the case and the effect of the centrifugal forces on the locking element, in the event of partial bolt loosening, prevents this bolt from rotating because the bolthead is constrained by resting against the case base.
More specifically, the device proposed by the invention is characterized in that it comprises a case positioned between the roots of a pair of blades and has a cross-section matching that of the channel. The case includes a lower base situated above the channel bottom and a cross-sectionally non-circular, radial, traverse aperture. The locking element is adapted to slide within the aperture when acted on by the drive bolt. The bolthead dimensions are such that it shall remain trapped between the channel bottom and the case base.
Preferably the device also includes means restricting the rise of the locking element.
The means limiting the rise of the locking element are fitted with cooperating stop surfaces matching the locking element and the case.
Advantageously the locking element may be retracted into the case. This feature assures that the device may slide inside the channel during assembly.
Other advantages and features of the invention are elucidated in the following, illustrative and non-limiting description and in relation to the attached drawings.